Hydraulic systems may include one or more valves for controlling the flow of hydraulic fluid to one or more fluid-operated devices. For example, a machine may include one or more fluid-operated actuators that may be controlled by the hydraulic system for performing work. One way in which the operation of the valves in the hydraulic system can be controlled is based on the pressure in the one or more fluid operated devices, such as, for example hydraulic actuators. In particular, the opening and closing of the fluid passages by the valves may be selectively controlled to control the pressure in the hydraulic actuators.
Typically, the valves used for controlling the flow of hydraulic fluid in such hydraulic systems have an open loop configuration. This means that operation of the valve is controlled by inputting a setting to, for example, a biasing element such as a spring that acts on the valve. While such valves may be adequate for many applications, they may not be able to provide as precise of control in some applications, particularly those that involve a high flow or high pressure operating range. Additionally, the operation of such valves in these applications can become unstable further impairing the accuracy of the valves.